An aqueous solution of CCA (a wood preservative composed of chromium, copper and arsenic) and creosote oil have been typical of the chemicals used for protecting wood against decay and damage by worms to increase its durability.
These chemicals are good preservatives, but have no property that protects wood from cracking. Wood treated with such chemicals is very likely to crack and split, as any untreated wood is.
It is impossible within the range of practically available techniques to make any such chemical uniformly impregnate the center of a piece of wood sized for practical use such as for a building, e.g., a square block of wood or a wooden brick. The interior of a piece of wood remains for the greater part untreated, and as a crack will allow rainwater, rotting fungi, etc. to enter, it will have a decayed interior despite its sound outward appearance, and will therefore offer unexpectedly low durability.
CCA is regarded as a harmful substance, since it is a highly toxic chemical which develops a green color, and there are even regions where its use is prohibited. Such problems with CCA are pointed out in Japanese Patent Laid-Open Application (KOKAI) under No. 63-199603.
Creosote oil has only a low degree of permeation into wood having a high water content, since it is lipophilic and hydrophobic. It also has the disadvantage of leaving a post-treatment residue, a black oily substance which may stain clothes, etc.
Japanese Patent Laid-Open Application (KOKAI) under No. 63-231902 describes a method of improving the drawbacks of wood, i.e., liability to decay, flammability, and dimensional instability, which comprises impregnating wood with an organic substance (e.g., barium chloride, or boric acid in an aqueous solution), and simultaneously or separately coating or impregnating it with a resin (e.g. a urea resin, or polyethylene glycol methacrylate). These chemicals and processing methods, however, enable impregnation only through the surface layer of wood, and are incapable of permeating the center of a thick block of material, such as a wooden brick.
Compounds such as polyethylene glycol permeate wood easily because of their high power ability to absorb water, but are also very likely to flow away, and are therefore defective from a durability standpoint. A previous invention made by the inventors of the present invention, described in Japanese Patent Laid-Open Application (KOKAI) under No. 2-98403, employs an organic solvent and a curable synthetic resin in combination with a dimensional stabilizer. The use of an organic solvent, however, calls for the full drying of the material to be impregnated, and the material is likely to crack during its drying.
For example, a wooden brick formed from a material with a core and having a high water content shrinks so heavily as it is dried that, upon drying, it may have a large open crack. Such a large crack mars the appearance of the brick not only before, but also after its use for a particular purpose in construction, and is also detrimental to its durability. The susceptibility to cracking and low durability of wooden bricks lower their evaluation and obstruct the growth of their use despite the various advantages that they have as wood products.
The conventional methods have therefore been applicable only to thin sheets of wood to be superposed on, and bonded to a surface, e.g. plywood.
Compounds of phosphoric acids such as ammonium phosphates and guanidine phosphates, and dicyandiamide are examples of known flame retardants for wood. These flame retardants, however, have the drawback of being low in the property of giving dimensional stability to wood, allowing it to crack. Dimensional stabilizers, such as polyethylene glycol, are flammable, and cannot be used with any flame retardant, since they exert a negative effect on the purpose for which the flame retardant is employed. They also have the drawback of flowing away easily from wood.
It is an object of this invention to overcome the drawbacks of the prior art as hereinabove pointed out, and to provide a composition for treating wood to prevent cracking, give it dimensional stability, protect it against decay and damage by termites and render it nonflammable, and to provide wood treated with the same. More particularly, it is an object of this invention to provide a wood processing composition and method which ensure that no cracking, etc. occurs even to a material having a high water content during its drying prior to treatment, thereby providing high quality processed wood.